Rubber additives such as pigments, fillers, reinforcement agents, processing aids and the like are generally processed to be highly dispersible in rubber compositions. In the past, such additives were made highly dispersible by being formed into fine powders. These fine powders, although meeting the requirements of being easily dispersible, pose significant problems in handling and may potentially cause health problems for workers who are exposed to the dust products of these materials.
The use of silica additives has become increasingly important to the rubber industry. Silica, which may be in the form of silica pigments, is commonly used in the rubber industry to provide reinforcing and stiffening properties to various types of rubber compositions. Additionally, incorporating silica into rubber compositions has been found to be advantageous in that such compositions do not deteriorate under heating as rapidly as do most other rubber additives.
Silica in a free flowing powder form will disperse readily into rubber compounds. However, when utilizing conventional silica products, their dustiness becomes a problem due to the handling and compounding of rubber formulations. Concerns by manufacturers who utilize any small particle size material, such as silica pigment, have led to the development of more dust-free forms of such products.
The most common method used to reduce the dustiness of compounds is particle agglomeration or pelletization. A pelletized product is easily handled in a production environment and creates little dust.
A pelletized version of precipitated silica will minimize dust problems and facilitate handling and therefore would be highly desirable to rubber manufacturers. However, there remains an important requirement that such a pelletized form of the silica must break down and redisperse in the powder form. Attempts to improve silica products for use in rubber manufacturing include chemically treating silica in order to affect good dispersibility. Heretofore an acceptable dust-free, highly dispersible pelletized form of rubber additive, particularly silica, has not been developed for the rubber industry.
The present invention addresses the need of a dust-free, highly dispersible pelletized form of silica and is directed to a unique process and apparatus by which such silica may be produced.